Method for manufacturing light-emitting element

ABSTRACT

A method for manufacturing a light-emitting element includes forming a first light-emitting part, forming a tunnel junction part on the first light-emitting part, and forming a second light-emitting part on the tunnel junction part. The step of forming the first light-emitting part includes forming a first layer with a first p-type impurity concentration at a first temperature, and forming a second layer with a second p-type impurity concentration on the first layer. The second p-type impurity concentration is greater than the first p-type impurity concentration. The step of forming the second light-emitting part includes forming a third layer with a third p-type impurity concentration at a second temperature and forming a fourth layer with a fourth p-type impurity concentration on the third layer. The fourth p-type impurity concentration is greater than the third p-type impurity concentration. The second temperature is less than the first temperature.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims priority to Japanese PatentApplication No. 2021-116174, filed on Jul. 14, 2021, the entire contentsof which are incorporated herein by reference.

FIELD

The present disclosure relates to a method for manufacturing alight-emitting element.

BACKGROUND

Japanese Patent Application No. 2004-128502 describes, for example, alight-emitting element that includes: a first light-emitting part thatincludes a first n-type layer, a first active layer, and a first p-typelayer; a tunnel junction layer located on the first light-emitting part;and a second light-emitting part that is located on the tunnel junctionlayer and includes a second n-type layer, a second active layer, and asecond p-type layer.

SUMMARY

According to one aspect of the present invention, a method formanufacturing a light-emitting element includes forming a firstlight-emitting part, forming a tunnel junction part on the firstlight-emitting part; and forming a second light-emitting part on thetunnel junction part. The first light-emitting part includes a firstn-type semiconductor layer, a first active layer located on the firstn-type semiconductor layer, and a first p-type semiconductor layerlocated on the first active layer.

The second light-emitting part includes a second n-type semiconductorlayer, a second active layer located on the second n-type semiconductorlayer, and a second p-type semiconductor layer located on the secondactive layer. The first p-type semiconductor layer includes a firstlayer and a second layer. The forming of the first light-emitting partincludes forming the first layer with a first p-type impurityconcentration at a first temperature, and forming the second layer witha second p-type impurity concentration on the first layer. The secondp-type impurity concentration is greater than the first p-type impurityconcentration. The second p-type semiconductor layer includes a thirdlayer and a fourth layer. The forming of the second light-emitting partincludes forming the third layer with a third p-type impurityconcentration at a second temperature and forming the fourth layer witha fourth p-type impurity concentration on the third layer. The fourthp-type impurity concentration is greater than the third p-type impurityconcentration.

The second temperature is less than the first temperature.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing a light-emitting elementaccording to an embodiment;

FIG. 2 is a flowchart showing a method for manufacturing thelight-emitting element according to the embodiment;

FIG. 3A is a flowchart showing details of a process of forming a firstp-type semiconductor layer of FIG. 2 ;

FIG. 3B is a flowchart showing details of a process of forming a secondp-type semiconductor layer of FIG. 2 ;

FIG. 4 is a cross-sectional view of a first light-emitting part obtainedby a process of forming the first light-emitting part according to themethod for manufacturing the light-emitting element according to theembodiment;

FIG. 5 is a cross-sectional view for describing a tunnel junction partobtained by a process of forming the tunnel junction part according tothe method for manufacturing the light-emitting element according to theembodiment;

FIG. 6 is a cross-sectional view for describing a second light-emittingpart obtained by a process of forming the second light-emitting partaccording to the method for manufacturing the light-emitting elementaccording to the embodiment;

FIG. 7 is a cross-sectional view for describing a n-side electrode and ap-side electrode obtained by a process of forming the n-side electrodeand the p-side electrode according to the method for manufacturing thelight-emitting element according to the embodiment;

FIG. 8A is a graph showing a relationship between a second temperatureand a forward voltage Vf of light-emitting elements for examples andreference examples; and

FIG. 8B is a graph showing a relationship between the second temperatureand an output Po of the light-emitting elements for the examples and thereference examples.

DETAILED DESCRIPTION

Exemplary embodiments will now be described with reference to thedrawings. The drawings are schematic or conceptual, and therelationships between the thickness and width of portions, theproportional coefficients of sizes among portions, etc., are notnecessarily the same as the actual values thereof. Furthermore, thedimensions and proportions of elements may be illustrated differentlyamong drawings, even for identical elements. In the specification of theapplication and the drawings, components similar to those described inregard to a previous drawing are marked with similar reference numerals,and a repeated detailed description is omitted as appropriate. Foreasier understanding of the following description, the arrangements andconfigurations of the portions are described using an XYZ orthogonalcoordinate system. An X-axis, a Y-axis, and a Z-axis are orthogonal toeach other. The direction in which the X-axis extends is taken as an“X-direction”, the direction in which the Y-axis extends is taken as a“Y-direction”, and the direction in which the Z-axis extends is taken asa “Z-direction.” Although the Z-direction is taken as up and theopposite direction is taken as down for easier understanding of thedescription, these directions are independent of the direction ofgravity.

FIG. 1 is a cross-sectional view showing a light-emitting elementaccording to an embodiment.

The light-emitting element 10 according to this embodiment includes asubstrate 11, a semiconductor stacked body 12, an n-side electrode 13,and a p-side electrode 14. The components of the light-emitting element10 will now be elaborated.

According to this embodiment, the substrate 11 has a flat plate shape.The upper surface and the lower surface of the substrate 11 aresubstantially parallel to the XY plane. However, multiple protrusionsmay be formed in the upper surface of the substrate. Although notparticularly limited, for example, sapphire (Al₂O₃), silicon (Si),silicon carbide (SiC), gallium nitride (GaN), etc., are examples of thematerial of the substrate 11. According to the present embodiment, thesubstrate 11 is made of sapphire.

The semiconductor stacked body 12 is located on the substrate 11.

The semiconductor stacked body 12 is, for example, a stacked body inwhich multiple semiconductor layers made of nitride semiconductors arestacked. Here, “nitride semiconductor” includes all compositions ofsemiconductors for which the composition ratios x and y of the chemicalformula In_(x)Al_(y)Ga_(1-x-y)N (0≤x≤1, 0≤y≤1, and x+y≤1) are changedwithin the ranges respectively.

The semiconductor stacked body 12 includes a first light-emitting part110, a tunnel junction part 120, and a second light-emitting part 130.Generally speaking, the first light-emitting part 110 includes a firstn-type semiconductor layer 112, a first active layer 113, and a firstp-type semiconductor layer 114. The first light-emitting part 110 mayfurther include a foundation layer 111. The first p-type semiconductorlayer 114 includes a first layer 114 b and a second layer 114 c.Generally speaking, the second light-emitting part 130 includes a secondn-type semiconductor layer 131, a second active layer 132, and a secondp-type semiconductor layer 133. The second p-type semiconductor layer133 includes a third layer 133 b and a fourth layer 133 c. The firstp-type semiconductor layer 114 may further include a fifth layer 114 a.The second p-type semiconductor layer 133 may further include a sixthlayer 133 a. The components will now be elaborated.

The foundation layer 111 of the first light-emitting part 110 is locatedon the substrate 11. The foundation layer 111 includes, for example, anundoped semiconductor layer. In the specification, “undoped” means thatan n-type impurity and/or a p-type impurity is not intentionally doped.The term “n-type impurity” means an impurity that forms donors. The term“p-type impurity” means an impurity that forms acceptors. There arecases in which an undoped semiconductor layer that is adjacent to alayer intentionally doped with an n-type impurity and/or a p-typeimpurity includes the n-type impurity and/or the p-type impurity due todiffusion from the adjacent layer, etc. The undoped semiconductor layeris a semiconductor layer formed without supplying a source gas thatincludes an n-type impurity and/or a p-type impurity.

The undoped semiconductor layer of the foundation layer 111 includes,for example, gallium nitride (GaN).

The first n-type semiconductor layer 112 is located on the foundationlayer 111. However, the first n-type semiconductor layer may be directlylocated on the substrate without including the foundation layer in thefirst light-emitting part.

The first n-type semiconductor layer 112 includes one or more n-typesemiconductor layers. The n-type semiconductor layer of the first n-typesemiconductor layer 112 includes, for example, GaN doped with silicon(Si) as the n-type impurity. The n-type semiconductor layers of thefirst n-type semiconductor layer 112 may further include indium (In),aluminum (Al), etc.

The first n-type semiconductor layer 112 may further include one or moreundoped semiconductor layers. The undoped semiconductor layers of thefirst n-type semiconductor layer 112 include, for example, GaN.

The upper surface of the first n-type semiconductor layer 112 includes afirst surface 112 s 1, a second surface 112 s 2, and a third surface 112s 3. The first surface 112 s 1 is substantially parallel to the

X-Y plane. The second surface 112 s 2 is positioned higher than thefirst surface 112 s 1 and is substantially parallel to the X-Y plane.The second surface 112 s 2 is next to the first surface 112 s 1 in theX-direction in a top-view. The third surface 112 s 3 is positionedbetween the first surface 112 s 1 and the second surface 112 s 2 and issubstantially parallel to the Y-Z plane.

The first active layer 113 is located on the second surface 112 s 2.However, the shape of the upper surface of the first n-typesemiconductor layer is not limited to the shapes described above.

The first active layer 113 includes, for example, a multi-quantum wellstructure that includes multiple well layers and multiple barrierlayers. The multiple well layers can include, for example, indiumgallium nitride (InGaN). The multiple barrier layers can include, forexample, GaN. The well layer and the barrier layer may be, for example,undoped semiconductor layers. An n-type impurity and/or a p-typeimpurity may be included in at least portions of the well layer and thebarrier layer.

The first p-type semiconductor layer 114 is located on the first activelayer 113.

According to this embodiment, the first p-type semiconductor layer 114includes the fifth layer 114 a, the first layer 114 b, and the secondlayer 114 c in this order from the first active layer 113 side.

The fifth layer 114 a is located on the first active layer 113. Thefifth layer 114 a includes, for example, aluminum gallium nitride(AlGaN) doped with magnesium (Mg) as the p-type impurity.

The first layer 114 b is located on the fifth layer 114 a. The firstlayer 114 b is a semiconductor layer having a first p-type impurityconcentration. The first layer 114 b includes, for example, undoped GaN.By the first p-type semiconductor layer 114 including the undoped firstlayer 114 b, the electrostatic breakdown voltage characteristics of thelight-emitting element 10 can be improved compared to when the firstlayer 114 b is a semiconductor layer that includes a p-type impurity.The first p-type impurity concentration can be, for example, not lessthan 1×10¹⁹/cm³ and not more than 5×10¹⁹/cm³.

The second layer 114 c is located on the first layer 114 b. The secondlayer 114 c is a semiconductor layer having a second p-type impurityconcentration that is greater than the first p-type impurityconcentration. The second layer 114 c includes, for example, GaN dopedwith Mg as the p-type impurity. The tunnel junction part 120 is locatedon the second layer 114 c. The second p-type impurity concentration canbe, for example, not less than 5×10¹⁹/cm³ and not more than 1×10²¹/cm³.

Although the fifth layer 114 a and the second layer 114 c areintentionally doped with a p-type impurity, the first layer 114 b is notintentionally doped with a p-type impurity. Therefore, the p-typeimpurity concentrations of the fifth layer 114 a and the second layer114 c are greater than the impurity concentration of the first layer 114b. Also, the first layer 114 b may include a p-type impurity due to thep-type impurities of the fifth and second layers 114 a and 114 cdiffusing into the first layer 114 b.

A film thickness d12 of the first layer 114 b is greater than a filmthickness d13 of the second layer 114 c. The film thickness d13 of thesecond layer 114 c is greater than a film thickness d11 of the fifthlayer 114 a. In other words, film thickness d12>film thickness d13>filmthickness d11. However, the magnitude relationship of the filmthicknesses of the fifth layer 114 a, the first layer 114 b, and thesecond layer 114 c is not limited to the relationship described above.The film thickness d12 of the first layer 114 b can be, for example, notless than 30 nm and not more than 70 nm. The film thickness d13 of thesecond layer 114 c can be, for example, not less than 10 nm and not morethan 30 nm. The film thickness d11 of the fifth layer 114 a can be, forexample, not less than 5 nm and not more than 25 nm.

A configuration is described above in which the first p-typesemiconductor layer 114 includes the fifth layer 114 a, the first layer114 b, and the second layer 114 c. However, the configuration of thefirst p-type semiconductor layer is not limited to the configurationdescribed above as long as the first p-type semiconductor layer includesthe first and second layers.

The tunnel junction part 120 includes an n-type impurity and/or a p-typeimpurity. Specifically, the tunnel junction part 120 includes at leastone of a p-type semiconductor layer that has a higher p-type impurityconcentration than the semiconductor layer having the highest p-typeimpurity concentration among the semiconductor layers included in thefirst p-type semiconductor layer 114, or an n-type semiconductor layerthat includes a higher n-type impurity concentration than thesemiconductor layer having the highest n-type impurity concentrationamong the semiconductor layers included in a second n-type semiconductorlayer 131 described below. When a p-type semiconductor layer is includedin the tunnel junction part 120, the p-type semiconductor layerincludes, for example, GaN doped with Mg as the p-type impurity. When ann-type semiconductor layer is included in the tunnel junction part 120,the n-type semiconductor layer includes, for example, GaN doped with Sias the n-type impurity. According to this embodiment, the tunneljunction part 120 includes GaN doped with Si as the n-type impurity.

The second light-emitting part 130 is located on the tunnel junctionpart 120.

The second light-emitting part 130 includes the second n-typesemiconductor layer 131, the second active layer 132, and the secondp-type semiconductor layer 133.

The second n-type semiconductor layer 131 is located on the tunneljunction part 120. The second n-type semiconductor layer 131 includesone or more n-type semiconductor layers. The n-type semiconductor layersof the second n-type semiconductor layer 131 include, for example, GaNdoped with Si as the n-type impurity. The n-type semiconductor layers ofthe second n-type semiconductor layer 131 may further include In, Al,etc.

The second n-type semiconductor layer 131 may further include one ormore undoped semiconductor layers. Although the undoped semiconductorlayers of the second n-type semiconductor layer 131 are not particularlylimited, the undoped semiconductor layers include, for example, GaN.

The second active layer 132 is located on the second n-typesemiconductor layer 131.

The second active layer 132 includes, for example, a multi-quantum wellstructure that includes multiple well layers and multiple barrierlayers. The multiple well layers can include, for example, InGaN. Themultiple barrier layers can include, for example, GaN. The well layerand the barrier layer may be, for example, undoped semiconductor layers.An n-type impurity and/or a p-type impurity may be included in at leastportions of the well layer and the barrier layer.

The light that is emitted by the first and second active layers 113 and132 is, for example, ultraviolet light or visible light. The lightemission peak wavelength of the first active layer 113 and the lightemission peak wavelength of the second active layer 132 may bedifferent. Specifically, for example, the first active layer 113 mayemit blue light, and the second active layer 132 may emit green light.The light emission peak wavelength of the blue light is, for example,not less than 430 nm and not more than 490 nm. The light emission peakwavelength of the green light is, for example, not less than 500 nm andnot more than 540 nm.

The second p-type semiconductor layer 133 is located on the secondactive layer 132.

According to this embodiment, the second p-type semiconductor layer 133includes the sixth layer 133 a, the third layer 133 b, and the fourthlayer 133 c in this order from the second active layer 132 side.

The sixth layer 133 a is located on the second active layer 132. Thesixth layer 133 a includes, for example, AlGaN doped with Mg as thep-type impurity.

The third layer 133 b is located on the sixth layer 133 a. The thirdlayer 133 b is a semiconductor layer that has a third p-type impurityconcentration. The third layer 133 b includes, for example, undoped GaN.By the second p-type semiconductor layer 133 including the undoped thirdlayer 133 b, the electrostatic breakdown voltage characteristics of thelight-emitting element 10 can be improved compared to when the thirdlayer 133 b is a semiconductor layer that includes a p-type impurity.The third p-type impurity concentration can be, for example, not lessthan 1×10¹⁹/cm³ and not more than 5×10¹⁹/cm³.

The fourth layer 133 c is located on the third layer 133 b. The fourthlayer 133 c is a semiconductor layer having a fourth p-type impurityconcentration that is greater than the third p-type impurityconcentration. The fourth layer 133 c includes, for example, GaN dopedwith Mg as the p-type impurity. It is favorable for the fourth p-typeimpurity concentration to be less than the second p-type impurityconcentration. The fourth p-type impurity concentration can be, forexample, not less than 3×10¹⁹/cm³ and not more than 1×10²¹/cm³.

A film thickness d22 of the third layer 133 b is greater than a filmthickness d23 of the fourth layer 133 c. The film thickness d23 of thefourth layer 133 c is greater than a film thickness d21 of the sixthlayer 133 a. However, the magnitude relationship of the film thicknessesof the third, fourth, and sixth layers is not limited to therelationship described above. The film thickness d22 of the third layer133 b can be, for example, not less than 70 nm and not more than 110 nm.The film thickness d23 of the fourth layer 133 c can be, for example,not less than 10 nm and not more than 30 nm. The film thickness d21 ofthe sixth layer 133 a can be, for example, not less than 5 nm and notmore than 25 nm.

The film thickness d21 of the sixth layer 133 a is substantially equalto the film thickness d11 of the fifth layer 114 a.

The film thickness d22 of the third layer 133 b is greater than the filmthickness d12 of the first layer 114 b. In such a case, it is favorablefor the film thickness d22 to be not less than 1.5 times and not morethan 3 times the film thickness d12.

The film thickness d23 of the fourth layer 133 c is substantially equalto the film thickness d13 of the second layer 114 c. In summary, it isfavorable for film thickness d11=film thickness d21<film thicknessd13=film thickness d23<film thickness d12<film thickness d22. However,the magnitude relationship of these film thicknesses is not limited tosuch a relationship.

A configuration is described above in which the second p-typesemiconductor layer 133 includes the sixth layer 133 a, the third layer133 b, and the fourth layer 133 c. However, the second p-typesemiconductor layer 133 is not limited to the configuration describedabove as long as the second p-type semiconductor layer 133 includes thethird and fourth layers.

The n-side electrode 13 is located on a first surface 112 s 1 of thefirst n-type semiconductor layer 112. The n-side electrode 13 iselectrically connected to the first n-type semiconductor layer 112. Thep-side electrode 14 is located on the fourth layer 133 c of the secondp-type semiconductor layer 133. The p-side electrode 14 is electricallyconnected to the second p-type semiconductor layer 133.

A method for manufacturing the light-emitting element 10 according to anembodiment will now be described.

FIG. 2 is a flowchart showing the method for manufacturing thelight-emitting element according to this embodiment.

FIG. 3A is a flowchart showing details of the process of forming thefirst p-type semiconductor layer of FIG. 2 .

FIG. 3B is a flowchart showing details of the process of forming thesecond p-type semiconductor layer of FIG. 2 .

FIG. 4 is a cross-sectional view of the first light-emitting partobtained by the process of forming the first light-emitting partaccording to the method for manufacturing the light-emitting elementaccording to this embodiment.

FIG. 5 is a cross-sectional view for describing the tunnel junction partobtained by the process of forming the tunnel junction part according tothe method for manufacturing the light-emitting element according tothis embodiment.

FIG. 6 is a cross-sectional view for describing the secondlight-emitting part obtained by the process of forming the secondlight-emitting part according to the method for manufacturing thelight-emitting element according to this embodiment.

FIG. 7 is a cross-sectional view for describing the n-side electrode andthe p-side electrode obtained by the process of forming the n-sideelectrode and the p-side electrode according to the method formanufacturing the light-emitting element according to this embodiment.

Generally speaking, as shown in FIG. 2 , the method for manufacturingthe light-emitting element 10 according to this embodiment includes aprocess S1 of forming the first light-emitting part 110, a process S2 offorming the tunnel junction part 120, a process S3 of forming the secondlight-emitting part 130, and a process S4 of forming the n-sideelectrode 13 and the p-side electrode 14. The process S1 of forming thefirst light-emitting part 110 includes a process S12 of forming thefirst n-type semiconductor layer 112, a process S13 of forming the firstactive layer 113, and a process S14 of forming the first p-typesemiconductor layer 114. The process S1 of forming the firstlight-emitting part 110 may further include a process S11 of forming thefoundation layer 111. The process S3 of forming the secondlight-emitting part 130 includes a process S31 of forming the secondn-type semiconductor layer 131, a process S32 of forming the secondactive layer 132, and a process S33 of forming the second p-typesemiconductor layer 133.

As shown in FIG. 3A, the process S14 of forming the first p-typesemiconductor layer 114 includes a process S14 b of forming the firstlayer 114 b and a process S14 c of forming the second layer 114 c. Theprocess S14 of forming the first p-type semiconductor layer 114 mayfurther include a process S14 a of forming the fifth layer 114 a. Asshown in FIG. 3B, the process S33 of forming the second p-typesemiconductor layer 133 includes a process S33 b of forming the thirdlayer 133 b and a process S33 c of forming the fourth layer 133 c. Theprocess S33 of forming the second p-type semiconductor layer 133 mayfurther include a process S33 a of forming the sixth layer 133 a.

Hereinbelow, a temperature T1 b when forming the first layer 114 b iscalled a “first temperature T1 b.” A temperature T2 b when forming thethird layer 133 b is called a “second temperature T2 b.” A temperatureT1 c when forming the second layer 114 c is called a “third temperatureT1 c.” A temperature T2 c when forming the fourth layer 133 c is calleda “fourth temperature T2 c.” A temperature T1 a when forming the fifthlayer 114 a is called a “fifth temperature T1 a.” A temperature T2 awhen forming the sixth layer 133 a is called a “sixth temperature T2 a.”In the specification, “temperature” is a temperature measured by athermocouple located at the vicinity of the substrate 11.

For example, the first light-emitting part 110, the tunnel junction part120, and the second light-emitting part 130 included in thesemiconductor stacked body 12 are formed by MOCVD (metal organicchemical vapor deposition) in a furnace in which the pressure and thetemperature can be regulated. Specifically, the semiconductor stackedbody 12 is formed by supplying a carrier gas and a source gas to thefurnace.

For example, hydrogen (H₂) gas, nitrogen (N₂) gas, etc., can be used asthe carrier gas.

The source gas is selected as appropriate according to the semiconductorlayer to be formed. When a semiconductor layer that includes Ga isformed, for example, a source gas that includes Ga such astrimethylgallium (TMG) gas, triethylgallium (TEG) gas, or the like isused. When a semiconductor layer that includes N is formed, for example,a source gas that includes N such as ammonia (NH₃) gas or the like isused. When a semiconductor layer that includes Al is formed, forexample, a source gas that includes Al such as trimethylaluminum (TMA)gas or the like is used. When a semiconductor layer that includes In isformed, for example, a source gas that includes In such astrimethylindium (TMI) or the like is used. When a semiconductor layerthat includes Si is formed, for example, a gas that includes Si such asmonosilane (SiH₄) gas or the like is used. When a semiconductor layerthat includes Mg is formed, for example, a source gas that includes Mgsuch as bis cyclopentadienyl magnesium (Cp₂Mg) gas or the like is used.The processes will now be elaborated.

First, the process 51 of forming the first light-emitting part 110 isperformed.

The process S1 of forming the first light-emitting part 110 includes theprocess S11 of forming the foundation layer 111, the process S12 offorming the first n-type semiconductor layer 112 on the foundation layer111, the process S13 of forming the first active layer 113 on the firstn-type semiconductor layer 112 and the process S14 of forming the firstp-type semiconductor layer 114 on the first active layer 113 in thisorder.

The process S11 of forming the foundation layer 111 to the process S13of forming the first active layer 113 include forming the foundationlayer 111, the first n-type semiconductor layer 112, and the firstactive layer 113 on the substrate 11 in this order by supplying thecarrier gases and the source gases corresponding to each layer of thefoundation layer 111, the first n-type semiconductor layer 112, and thefirst active layer 113 to a furnace.

As shown in FIG. 3A, the process S14 of forming the first p-typesemiconductor layer 114 includes the process S14 a of forming the fifthlayer 114 a at the fifth temperature T1 a, the process S14 b of formingthe first layer 114 b at the first temperature T1 b, and the process S14c of forming the second layer 114 c at the third temperature T1 c inthis order.

In the process S14 a of forming the fifth layer 114 a, the fifth layer114 a is formed on the first active layer 113. For example, the fifthlayer 114 a is formed by supplying, to a furnace, a carrier gas, asource gas that includes Ga, Al, and N, and a source gas that includesthe p-type impurity of Mg. Thereby, the fifth layer 114 a that is madeof AlGaN doped with Mg as the p-type impurity is formed on the firstactive layer 113. The fifth temperature T1 a inside the furnace in theprocess S14 is not particularly limited. It is favorable for the fifthtemperature T1 a to be, for example, not less than 800° C. and not morethan 900° C.

In the process S14 b of forming the first layer 114 b, the first layer114 b of the first p-type impurity concentration is formed on the fifthlayer 114 a. For example, the first layer 114 b is formed by supplying,to a furnace, a carrier gas and a source gas that includes Ga and N butdoes not include a p-type impurity. In the process S14 b, the firstlayer 114 b is formed without supplying a source gas that includes ap-type impurity. Thereby, the first layer 114 b that is made of undopedGaN is formed on the fifth layer 114 a. It is favorable for the firsttemperature T1 b inside the furnace in the process S14 b to be greaterthan the fifth temperature T1 a when forming the fifth layer 114 a. Thefirst temperature T1 b inside the furnace in the process S14 b is notparticularly limited. It is favorable for the first temperature T1 b tobe, for example, not less than 900° C. and not more than 1050° C. Thecrystallinity of the first layer 114 b can be improved by setting thefirst temperature T1 b to be not less than 900° C. The thermal load onthe first active layer 113 can be reduced by setting the firsttemperature T1 b to be not more than 1050° C.

In the process S14 c of forming the second layer 114 c, the second layer114 c is formed on the first layer 114 b with the fourth p-type impurityconcentration that is greater than the first p-type impurityconcentration. For example, the second layer 114 c is formed bysupplying, to a furnace, a carrier gas that includes nitrogen gas, asource gas that includes Ga and N, and a source gas that includes thep-type impurity of Mg. Thereby, the second layer 114 c that is made ofGaN doped with Mg as the p-type impurity is formed on the first layer114 b. It is favorable for the third temperature T1 c inside the furnacein the process S14 c to be greater than the fifth temperature T1 a andless than the first temperature T1 b. In other words, it is favorablethat fifth temperature T1 a<third temperature T1 c<first temperature T1b. The third temperature T1 c inside the furnace in the process S14 c isnot particularly limited. It is favorable for the third temperature T1 cto be, for example, not less than 830° C. and not more than 980° C. Bysetting the third temperature T1 c to be not less than 830° C., thep-type impurity of a semiconductor layer doped with Mg as the p-typeimpurity can be easily activated. By setting the third temperature T1 cto be not more than 980° C., the diffusion of the p-type impurityincluded in the first p-type semiconductor layer 114 to the third layer133 b side can be reduced.

Thus, as shown in FIG. 4 , the first light-emitting part 110 thatincludes the foundation layer 111, the first n-type semiconductor layer112, the first active layer 113, and the first p-type semiconductorlayer 114 is formed on the substrate 11.

Then, the process S2 of forming the tunnel junction part 120 isperformed.

In the process S2 of forming the tunnel junction part 120, the tunneljunction part 120 is formed on the first light-emitting part 110. Forexample, the tunnel junction part 120 is formed by supplying, to afurnace, a carrier gas, a source gas that includes Ga and N, and asource gas that includes the n-type impurity of Si. Thereby, the tunneljunction part 120 that is made of GaN doped with Si as the n-typeimpurity is formed on the first light-emitting part 110. The tunneljunction part 120 may be formed by MBE (Molecular Beam Epitaxy) insteadof MOCVD.

Then, the process S3 of forming the second light-emitting part 130 isperformed.

As shown in FIG. 2 , the process S3 of forming the second light-emittingpart 130 includes the process S31 of forming the second n-typesemiconductor layer 131 on the tunnel junction part 120, the process S32of forming the second active layer 132 on the second n-typesemiconductor layer 131, and the process S33 of forming the secondp-type semiconductor layer 133 on the second active layer 132 in thisorder.

The process S31 of forming the second n-type semiconductor layer 131 tothe process S32 of forming the second active layer 132 include formingthe second n-type semiconductor layer 131 and the second active layer132 on the tunnel junction part 120 in this order by supplying, to afurnace, carrier gases and source gases corresponding to each layer ofthe second n-type semiconductor layer 131 and the second active layer132.

As shown in FIG. 3B, the process S33 of forming the second p-typesemiconductor layer 133 includes the process S33 a of forming the sixthlayer 133 a at the sixth temperature T2 a, the process S33 b of formingthe third layer 133 b at the second temperature T2 b, and the processS33 c of forming the fourth layer 133 c at the fourth temperature T2 cin this order.

In the process S33 a of forming the sixth layer 133 a, the sixth layer133 a is formed on the second active layer 132. For example, the sixthlayer 133 a is formed by supplying, to a furnace, a carrier gas, asource gas that includes Ga, Al, and N, and a source gas that includesthe p-type impurity of Mg. Thereby, the sixth layer 133 a that is madeof AlGaN doped with Mg is formed on the second active layer 132. Thesixth temperature T2 a inside the furnace in the process S33 a is, forexample, substantially equal to the fifth temperature T1 a when formingthe fifth layer 114 a.

In the process S33 b of forming the third layer 133 b, the third layer133 b of the third p-type impurity concentration is formed on the sixthlayer 133 a. For example, a carrier gas and a source gas that includesGa and N but does not include a p-type impurity is supplied to afurnace. In the process S33 b, the third layer 133 b is formed withoutsupplying a source gas that includes a p-type impurity. Thereby, thethird layer 133 b that is made of undoped GaN is formed on the sixthlayer 133 a.

If the second temperature T2 b is high in the process S33 b, the p-typeimpurity that is included in the first p-type semiconductor layer 114easily diffuses toward the third layer 133 b side. When the p-typeimpurity diffuses toward the third layer 133 b side and diffuses into,for example, the tunnel junction part 120, the electrons that aresupplied from the tunnel junction part 120 to the second light-emittingpart 130 are reduced, and a forward voltage Vf of the light-emittingelement 10 is increased. Conversely, according to this embodiment, thesecond temperature T2 b is less than the first temperature T1 b whenforming the first layer 114 b. Therefore, the diffusion of the p-typeimpurity doped into the first p-type semiconductor layer 114 toward thethird layer 133 b side can be reduced, and the p-type impurity diffusioninto the tunnel junction part 120 can be reduced. As a result, thelight-emitting element 10 can have a low forward voltage Vf.

On the other hand, if the second temperature T2 b is low, for example,the p-type impurities that are doped into the second layer 114 c, thefifth layer 114 a, and the sixth layer 133 a may not be sufficientlyactivated, and the crystallinity of the third layer 133 b may bereduced. Conversely, according to this embodiment, the secondtemperature T2 b is greater than the fifth temperature T1 a when formingthe fifth layer 114 a and the sixth temperature T2 a when forming thesixth layer 133 a. Therefore, the p-type impurities of the second layer114 c, the fifth layer 114 a, and the sixth layer 133 a can be easilyactivated, and the degradation of the crystallinity of the third layer133 b can be reduced.

In summary, it is favorable that first temperature T1 b>secondtemperature T2 b>fifth temperature T1 a and sixth temperature T2 a.However, second temperature T2 b fifth temperature T1 a and sixthtemperature T2 a is acceptable. The second temperature T2 b is notparticularly limited. It is favorable for the second temperature T2 b tobe, for example, not less than 900° C. and not more than 980° C. Bysetting the second temperature T2 b to be not less than 900° C., forexample, the p-type impurities of the second layer 114 c, the fifthlayer 114 a, and the sixth layer 133 a can be activated, and thecrystallinity of the third layer 133 b can be improved. By setting thesecond temperature T2 b to be not more than 980° C., the diffusion ofthe p-type impurity included in the first p-type semiconductor layer 114toward the third layer 133 b side can be reduced. It is favorable forthe difference between the first temperature T1 b and the secondtemperature T2 b to be not less than 20° C. and not more than 100° C.

According to this embodiment, the third layer 133 b is formed so thatthe film thickness d22 of the third layer 133 b is greater than the filmthickness d12 of the first layer 114 b. There are cases in which concavepits caused by dislocations, etc., are formed in the upper surface ofthe sixth layer 133 a. By setting the film thickness d22 of the thirdlayer 133 b to be thicker, such concave pits can be filled with thethird layer 133 b, and the upper surface of the third layer 133 b canapproach a flat surface. As a result, the crystallinity of the fourthlayer 133 c formed on the third layer 133 b can be improved. Also, thethermal load on the semiconductor layers formed before forming the thirdlayer 133 b can be reduced.

In the process S33 c of forming the fourth layer 133 c, the fourth layer133 c is formed on the third layer 133 b with the fourth p-type impurityconcentration that is greater than the third p-type impurityconcentration. For example, the fourth layer 133 c is formed bysupplying, to a furnace, a carrier gas, a source gas that includes Gaand N, and a source gas that includes the p-type impurity of Mg.Thereby, the fourth layer 133 c that is made of GaN doped with Mg isformed on the third layer 133 b. It is favorable for the fourthtemperature T2 c inside the furnace in the process S33 c to be greaterthan the sixth temperature T2 a when forming the sixth layer 133 a andless than the second temperature T2 b when forming the third layer 133b. For example, the fourth temperature T2 c is substantially equal tothe third temperature T1 c when forming the first layer 114 b.

In summary, it is favorable that fifth temperature T1 a =sixthtemperature T2 a<temperature T1 c =temperature T2 c<temperature T2b<temperature T1 b. However, the magnitude relationship of thetemperatures T1 a, T1 b, T1 c, T2 a, T2 b, and T2 c is not limited tosuch a relationship.

Thus, as shown in FIG. 6 , the second light-emitting part 130 is formedon the tunnel junction part 120.

Then, the process S4 of forming the n-side electrode 13 and the p-sideelectrode 14 is performed.

In the process S4 of forming the n-side electrode 13 and the p-sideelectrode 14, first, as shown in FIG. 7 , the first and third surfaces112 s 1 and 112 s 3 of the first n-type semiconductor layer 112 areexposed from under the tunnel junction part 120 and the secondlight-emitting part 130 by removing a portion of the semiconductorstacked body 12. For example, the portion of the semiconductor stackedbody 12 can be removed by selective etching using a resist.

Then, the n-side electrode 13 is formed on the exposed first surface 112s 1. Also, the p-side electrode 14 is formed on the fourth layer 133 cof the second p-type semiconductor layer 133. For example, the n-sideelectrode 13 and the p-side electrode 14 can be formed by sputtering orvapor deposition.

Thus, the light-emitting element 10 can be obtained as shown in FIG. 7 .However, the method for manufacturing the light-emitting element is notlimited to the methods described above. For example, the method formanufacturing the light-emitting element may be performed without theprocess of forming the foundation layer, and the first n-typesemiconductor layer may be directly formed on the substrate.

The method for manufacturing the light-emitting element 10 according tothis embodiment includes the process S1 of forming the firstlight-emitting part 110, the process S2 of forming the tunnel junctionpart 120 on the first light-emitting part 110, and the process S3 offorming the second light-emitting part 130 on the tunnel junction part120. The first light-emitting part 110 includes the first n-typesemiconductor layer 112, the first active layer 113 located on the firstn-type semiconductor layer 112, and the first p-type semiconductor layer114 located on the first active layer 113. The second light-emittingpart 130 includes the second n-type semiconductor layer 131, the secondactive layer 132 located on the second n-type semiconductor layer 131,and the second p-type semiconductor layer 133 located on the secondactive layer 132.

The first p-type semiconductor layer 114 includes the first layer 114 band the second layer 114 c. The process S1 of forming the firstlight-emitting part 110 includes the process 514 b of forming the firstlayer 114 b at the first temperature T1 b without supplying a source gasthat includes a p-type impurity, and the process S14 c of forming thesecond layer 114 c on the first layer 114 b by supplying a source gasthat includes a p-type impurity.

The second p-type semiconductor layer 133 includes the third layer 133 band the fourth layer 133 c. The process S3 of forming the secondlight-emitting part 130 includes the process S33 b of forming the thirdlayer 133 b at the second temperature T2 b that is less than the firsttemperature T1 b without supplying a source gas that includes a p-typeimpurity, and the process S33 c of forming the fourth layer 133 c on thethird layer 133 b by supplying a source gas that includes a p-typeimpurity.

The diffusion of the p-type impurity of the first p-type semiconductorlayer 114 mainly into the tunnel junction part 120 when forming thethird layer 133 b can be reduced thereby. As a result, thelight-emitting element 10 can have a low forward voltage Vf. It may beconsidered to reduce the growth temperatures of the semiconductor layersincluded in the second light-emitting part 130 that is formed after thetunnel junction part 120 to reduce the diffusion of the p-typeimpurities into the tunnel junction part 120. In the secondlight-emitting part 130 according to this embodiment, the secondtemperature T2 b of the third layer 133 b that is formed withoutsupplying a source gas that includes a p-type impurity is less than thefirst temperature T1 b. The diffusion of the p-type impurity of thefirst p-type semiconductor layer 114 into the tunnel junction part 120can be reduced thereby without greatly reducing the characteristics ofthe light-emitting element 10. For example, if the fourth temperature T2c of the fourth layer 133 c that is formed by supplying a source gasthat includes a p-type impurity is low, there is a possibility that theactivation of the p-type impurity of the fourth layer 133 c will not besufficient.

It is favorable for the film thickness d22 of the third layer 133 b tobe greater than the film thickness d12 of the first layer 114 b.Thereby, the concave pits of the upper surface of the sixth layer 133 acan be filled with the third layer 133 b, and the upper surface of thethird layer 133 b can approach a flat surface. As a result, thecrystallinity of the fourth layer 133 c formed on the third layer 133 bcan be improved. By setting the second temperature T2 b to be less thanthe first temperature T1 b, even when the film thickness d22 of thethird layer 133 b is thick, the thermal load on the semiconductor layersformed before forming the third layer 133 b can be reduced compared towhen the first temperature T1 b and the second temperature T2 b are thesame temperature. It is favorable for the film thickness d22 of thethird layer 133 b to be not less than 1.5 times the film thickness d12of the first layer 114 b. When the film thickness d22 of the third layer133 b is set to be not less than 1.5 times and not more than 3 times thefilm thickness d12 of the first layer 114 b, for example, it isfavorable for the film thickness d22 of the third layer 133 b to be 90nm, and it is favorable for the film thickness d12 of the first layer114 b to be 50 nm.

The first p-type semiconductor layer 114 further includes the fifthlayer 114 a. The process Si of forming the first light-emitting part 110further includes the process 514 a of forming the fifth layer 114 a bysupplying a source gas that includes the p-type impurity before theprocess 514 b of forming the first layer 114 b. The quantity of holesinjected into the first active layer 113 can be increased by providingthe fifth layer 114 a. The second p-type semiconductor layer 133 furtherincludes the sixth layer 133 a. The process S3 of forming the secondlight-emitting part 130 further includes the process S33 a of formingthe sixth layer 133 a by supplying a source gas that includes a p-typeimpurity before the process S33 b of forming the third layer 133 b. Thequantity of holes injected into the second active layer 132 can beincreased by providing the sixth layer 133 a.

In the process 514 c of forming the second layer 114 c, the second layer114 c is formed at the third temperature T1 c that is less than thefirst temperature T1 b when forming the first layer 114 b and the secondtemperature T2 b when forming the third layer 133 b. Thereby, thediffusion of the p-type impurity of the fifth layer 114 a toward thesecond layer 114 c side can be reduced when forming the second layer 114c. In the process S33 c of forming the fourth layer 133 c, the fourthlayer 133 c is formed at the fourth temperature T2 c that is less thanthe first temperature T1 b when forming the second layer 114 c and thesecond temperature T2 b when forming the third layer 133 b. Thereby, thediffusion of the p-type impurities of the second and fifth layers 114 cand 114 a into the tunnel junction part 120 can be reduced when formingthe fourth layer 133 c.

EXAMPLES

Examples and reference examples will now be described.

Light-emitting elements according to examples 1 to 5 and light-emittingelements according to reference examples 1 and 2 were made.

The light-emitting elements according to the examples 1 to 5 and thelight-emitting elements according to the reference examples 1 and 2 eachhad layer structures similar to the light-emitting element 10 shown inFIG. 1 . The second temperature when forming the third layer of thesecond p-type semiconductor layer was different between thelight-emitting elements according to the examples 1 to 5 and thelight-emitting elements according to the reference examples 1 and 2, andthe same formation methods of the other layers of the first p-typesemiconductor layer including the first layer were used. Specifically,the first p-type semiconductor layers of the light-emitting elementsaccording to the examples 1 to 5 and the light-emitting elementsaccording to the reference examples 1 and 2 each included the fifth,first, and second layers similarly to the first p-type semiconductorlayer 114 of FIG. 1 . The second p-type semiconductor layers of thelight-emitting elements according to the examples 1 to 5 and thelight-emitting elements according to the reference examples 1 and 2 eachincluded the sixth, third, and fourth layers similarly to the secondp-type semiconductor layer 133 of FIG. 1 .

The fifth layer and the sixth layer each were made of AlGaN doped withMg as the p-type impurity. The fifth layer and the sixth layer each wereformed by CVD by supplying a carrier gas, a source gas that included Al,Ga, and N, and a source gas that included Mg. The fifth temperature T1 awhen forming the fifth layer was set to 840° C. The sixth temperature T2a when forming the sixth layer was set to 840° C.

The first layer and the third layer each included GaN. The first layerand the third layer each were formed by CVD by supplying a carrier gasand a source gas that included Ga and N. A source gas that included Mgwas not supplied when forming the first and third layers. The firsttemperature T1 b when forming the first layer was set to 1000° C. Thesecond temperature T2 b when forming the third layer of the example 1was set to 900° C. The second temperature T2 b of the example 2 was setto 920° C. The second temperature T2 b of the example 3 was set to 940°C. The second temperature T2 b of the example 4 was set to 960° C. Thesecond temperature T2 b of the example 5 was set to 980° C. The secondtemperature T2 b of the reference example 1 was set to the same 1000° C.as the first temperature T1 b. The second temperature T2 b of thereference example 2 was set to 1020° C. which was greater than the firsttemperature T1 b.

The second layer and the fourth layer were made of GaN doped with Mg asa p-type impurity. The second layer and the fourth layer each wereformed by CVD by supplying a carrier gas, a source gas that included Gaand N, and a source gas that included Mg. The third temperature T1 cwhen forming the second layer was set to 910° C. The fourth temperatureT2 c when forming the fourth layer was set to 910° C.

FIG. 8A is a graph showing the relationship between the secondtemperature and the forward voltage Vf of the light-emitting element forthe examples and the reference examples.

FIG. 8B is a graph showing the relationship between the secondtemperature and an output Po of the light-emitting element for theexamples and the reference examples.

The forward voltage Vf and the output Po were measured for each of thelight-emitting elements according to the examples 1 to 5 and thelight-emitting elements according to the reference examples 1 and 2 thatwere made. The results are shown in FIGS. 8A and 8B.

As shown in FIG. 8A, compared to the light-emitting element according tothe reference example 1 in which the second temperature T2 b was thesame 1000° C. as the first temperature T1 b, the forward voltage Vf waslower for the light-emitting elements according to the examples 1 to 5in which the second temperature T2 b was at least 20° C. less than thefirst temperature T1 b, that is, the second temperature T2 b was set tobe not more than 980° C. As shown in FIG. 8B, the output Po was higherfor the light-emitting elements 10 according to the examples 1 to 5 thanfor the light-emitting element of the reference example 1. On the otherhand, as shown in FIG. 8A, compared to the light-emitting elementaccording to the reference example 1, the forward voltage Vf was higherfor the light-emitting element according to the reference example 2 inwhich the second temperature T2 b was 1020° C. which was greater thanthe first temperature T1 b. As shown in FIG. 8B, the output Po of thelight-emitting element according to the reference example 2 was lessthan that of the light-emitting element according to the referenceexample 1. Accordingly, it is favorable to set the second temperature T2b to be less than the first temperature T1 b, and it is more favorablefor the difference between the second temperature T2 b and the firsttemperature T1 b to be not less than 20° C. Also, it is favorable forthe second temperature T2 b to be not less than 900° C. and not morethan 980° C.

What is claimed is:
 1. A method for manufacturing a light-emittingelement, the method comprising: forming a first light-emitting part, thefirst light-emitting part comprising: a first n-type semiconductorlayer, a first active layer located on the first n-type semiconductorlayer, and a first p-type semiconductor layer located on the firstactive layer, the first p-type semiconductor layer comprising a firstlayer and a second layer; forming a tunnel junction part on the firstlight-emitting part; and forming a second light-emitting part on thetunnel junction part, the second light-emitting part comprising: asecond n-type semiconductor layer, a second active layer located on thesecond n-type semiconductor layer, and a second p-type semiconductorlayer located on the second active layer, the second p-typesemiconductor layer comprising a third layer and a fourth layer;wherein: the step of forming the first light-emitting part comprises:forming the first layer with a first p-type impurity concentration at afirst temperature, and forming the second layer with a second p-typeimpurity concentration on the first layer, the second p-type impurityconcentration being greater than the first p-type impurityconcentration; and the forming of the second light-emitting partcomprises: forming the third layer with a third p-type impurityconcentration at a second temperature that is less than the firsttemperature, and forming the fourth layer with a fourth p-type impurityconcentration on the third layer, the fourth p-type impurityconcentration being greater than the third p-type impurityconcentration.
 2. The method according to claim 1, wherein: a filmthickness of the third layer is greater than a film thickness of thefirst layer.
 3. The method according to claim 1, wherein: the step offorming the first layer comprises forming the first layer withoutsupplying a source gas including a p-type impurity; the step of formingthe second layer comprises forming the second layer by supplying asource gas including a p-type impurity; the step of forming the thirdlayer comprises forming the third layer without supplying a source gasincluding a p-type impurity; and the step of forming the fourth layercomprises forming the fourth layer by supplying a source gas including ap-type impurity.
 4. The method according to claim 2, wherein: the stepof forming the first layer comprises forming the first layer withoutsupplying a source gas including a p-type impurity; the step of formingthe second layer comprises forming the second layer by supplying asource gas including a p-type impurity; the step of forming the thirdlayer comprises forming the third layer without supplying a source gasincluding a p-type impurity; and the step of forming the fourth layercomprises forming the fourth layer by supplying a source gas including ap-type impurity.
 5. The method according to claim 1, wherein: the firstp-type semiconductor layer further comprises a fifth layer; the step offorming the first light-emitting part further comprises, before the stepof forming the first layer, forming the fifth layer by supplying asource gas including a p-type impurity; the second p-type semiconductorlayer further comprises a sixth layer; and the step of forming thesecond light-emitting part further comprises, before the step of formingthe third layer, forming the sixth layer by supplying a source gasincluding a p-type impurity.
 6. The method according to claim 2,wherein: the first p-type semiconductor layer further comprises a fifthlayer; the step of forming the first light-emitting part furthercomprises, before the step of forming the first layer, forming the fifthlayer by supplying a source gas including a p-type impurity; the secondp-type semiconductor layer further comprises a sixth layer; and the stepof forming the second light-emitting part further comprises, before thestep of forming the third layer, forming the sixth layer by supplying asource gas including a p-type impurity.
 7. The method according to claim3, wherein: the first p-type semiconductor layer further comprises afifth layer; the step of forming the first light-emitting part furthercomprises, before the step of forming the first layer, forming the fifthlayer by supplying a source gas including a p-type impurity; the secondp-type semiconductor layer further comprises a sixth layer; and the stepof forming the second light-emitting part further comprises, before thestep of forming the third layer, forming the sixth layer by supplying asource gas including a p-type impurity.
 8. The method according to claim1, wherein: a difference between the first temperature and the secondtemperature is not less than 20° C. and not more than 100° C.
 9. Themethod according to claim 2, wherein: a difference between the firsttemperature and the second temperature is not less than 20° C. and notmore than 100° C.
 10. The method according to claim 1, wherein: thefirst temperature is not less than 900° C. and not more than 1050° C.;and the second temperature is not less than 900° C. and not more than980° C.
 11. The method according to claim 2, wherein: the firsttemperature is not less than 900° C. and not more than 1050° C.; and thesecond temperature is not less than 900° C. and not more than 980° C.12. The method according to claim 1, wherein: the second layer is formedat a third temperature that is less than the first and secondtemperatures; the fourth layer is formed at a fourth temperature that isless than the first and second temperatures.
 13. The method according toclaim 2, wherein: the second layer is formed at a third temperature thatis less than the first and second temperatures; the fourth layer isformed at a fourth temperature that is less than the first and secondtemperatures.
 14. The method according to claim 3, wherein: the secondlayer is formed at a third temperature that is less than the first andsecond temperatures; the fourth layer is formed at a fourth temperaturethat is less than the first and second temperatures.
 15. The methodaccording to claim 1, wherein: a film thickness of the third layer isnot less than 1.5 times and not more than 3 times a film thickness ofthe first layer.
 16. The method according to claim 2, wherein: a filmthickness of the third layer is not less than 1.5 times and not morethan 3 times a film thickness of the first layer.
 17. The methodaccording to claim 1, further comprising: after the step of forming thesecond light-emitting part, forming a p-side electrode on the fourthlayer of the second p-type semiconductor layer, and forming an n-sideelectrode on the first n-type semiconductor layer.
 18. The methodaccording to claim 2, further comprising: after the step of forming thesecond light-emitting part, forming a p-side electrode on the fourthlayer of the second p-type semiconductor layer, and forming an n-sideelectrode on the first n-type semiconductor layer.